Variability in Planktonic Flora Density in Three Fixed Seasons in the Luanda Bay Area
Paulo Coelho
ABSTRACT
This work aimed to study the variability of planktonic flora, environmental data and phytoplankton species that cause Harmful Algae Blooms (HAB), in fixed stations of Luanda (8º44.30S; 13º16.56E), Floresta (8º46.77S; 13º15.43E) and Porto Pesqueiro (8º47.07S; 13º16.25E) in the area of the Bay of Luanda. The samples were collected during the period from February to December 2014, together with meteorological data and physico-chemical parameters of water (transparency, water temperature, and salinity) on the surface. A total of 164 microalgae taxa were found, being the predominant community made up of Dinophyceae and Bacillariophyceae in the forest and fishing port (inner bay), Bacillariophyceae and Dinophyceae at the fixed station Luanda. The Bacillariophyceae and Dinophyceae classes dominated the study area, while Chrysophyceae, Cyanophyceae and Euglenophyceae contributed little in phytoplankton composition during the study period in terms of abundance. The most abundant species for Bacillariophyceae were Leptocylindrus danicus, Chaetoceros spp, Asterionella glacialis, Skeletonema costatum and for Dinophyceae the Alexandrium tamarense, Prorocentrum micans, Protoperidinium spp, and Gonyaulax sp. The species Prorocentrum micans and Alexandrium tamarense, belonging to the group Dinophyta, were more abundant and dominant, especially in the dry season. The largest phytoplankton densities occurred in the dry season, which coincided with a reduction in richness and phytoplankton species diversity in the study area. The presence of Alexandrium tamarenses, Dinophysis acuminata, Pseudo-nitzschia spp and Gambierdiscus toxicus indicates the presence of potentially toxic species, and there may be possible problems to public health if that ecosystem is not monitored
